Tool for Surface Finish Machining

ABSTRACT

A tool ( 1 ) for surface finish machining, having a cushion ( 6 ) made of an elastic plastics foam, on the underside of which there is formed a working medium face ( 2 ) having working media or adhesives ( 8, 11, 12, 13 ) for the releasable attachment of working medium discs and on the top side of which there is formed a drive receptacle ( 4, 5 ) for application of work, is created as a product that is producible easily and non-critically in high volume, is extremely robust in use, is moisture-resistant and is able to withstand high rotational speeds, in that the elastic plastics foam consists of closed-cell expanded and fused-together particles of a thermoplastic elastomer (TPE).

Tools for surface finish machining such as grinding or polishing have been in use for a long time as manual tools with a grip or similar drive receptacle at the topside, now however mostly as mechanical tools with a mechanical drive receptacle or coupling for use with machines. At the bottom side, the tools are provided with working materials, for example, with an abrasive layer or with abrasive lamellas or instead with a coupling agent layer, for example, in the form of a coating of an adhesive or a hooking layer for a hook and loop fastener in order to attach working material discs in a detachable way. Likewise, mechanical clamping or holding means for working material discs are in use. In this context, the terms “topside” and “bottom side” refer only for illustration purposes to a preferred position of use during machining of a surface from above and do not preclude a use of the tool for finish machining slanted, vertical or even downwardly facing surfaces.

For a more uniform pressure distribution in surface finish machining and also for absorbing an accentuated or edge-emphasizing use of the tool, the tools usually have an elastic cushion on which the working material face is arranged and which is then located between the working material face and the drive receptacle. The required elasticity of the cushion is conventionally obtained by use of a polyurethane integral foam which is to be foamed in a mold. The integral foam which inherently is substantially open-celled is condensed at the surfaces, and in particular at edge surfaces, and provided with a molded skin that inhibits entry of moisture and dirt into the material. However, in use the molded skin is susceptible to injuries that then facilitate ingress of water and dirt into the integral foam. In particular the ingress of water, which occurs in case of use of the tool in the ambient and especially when wet grinding or wet polishing, causes overstressing of the material, material fatigue, and, in case of fast rotating tools, the destruction of the cushion by centrifugal forces. Already in case of cushions that are undamaged and not stressed by ingress of water, the centrifugal force loads, when using the tool as machines rotating at high rpm, can approach the loading capacity limit and can partially be held only by means of support measures by textile layers or the like applied to the working material face in combination with a working material layer or a coupling agent layer for working material discs. The integral foam of the cushion without support and securing action by the working material face would often “explode” already in the dry state, and even more so in the wet state.

Object of the invention is therefore to provide a tool which in respect to the requirements of a mass produced product can be manufactured easily and without problems while being robust and permanent and only little susceptible to loading by moisture and dirt as well as moreover providing greater safety margins when used with machines as a drive that rotate at high rpm.

According to the invention, this object is solved by tools according to the preamble of claim 1 based on the characterizing features of claim 1. The new configuration of the tool has shown that sweeping advantages can be achieved with a thermoplastic elastomer in the form of a material of closed-cell expanded and fused-together particles. Such a material, as it has been developed by the chemical industry, in particular by BASF SE, especially for lightweight and elastic soles of running shoes on the basis of urethane as so-called expanded thermoplastic polyurethane (E-TPU), can be employed in the tools only for surface finish machining as cushion material with a plurality of further advantages. These advantages exceed mostly the comparatively simple goals of intermediate soles of athletic shoes. Thus, the material with its closed-cell thin-wall particles is not only extremely lightweight and, depending on material adjustment, can reduce the total weight compared to the conventional PU integral foam to about one third. The material with its closed tenacious-elastic structure exhibits also extremely high tensile strength. This tensile strength makes it possible, for minimal specific weight of the material, to rate uncritical high rpm for a tool without a critical loading of the tool by the centrifugal forces having to be feared.

At the same time, this material surprisingly exhibits a functional range down to temperatures of minus 20° C. with good elasticity and excellent restoring capacities so that, in comparison to conventional tools with PU integral foam, no stiffening of the material or brittleness is to be feared even in case of work in the ambient.

The closed-cell constructed material requires no external molded skin against ingress of moisture or dirt. The closed cells without a particular protective envelopes are self-sealing and absorb in case of moisture only approximately one to two volume % of water. This eliminates for the tool the danger that an ingress of moisture or dirt is enabled due to rim damages of the cushion that easily occur during use. The tool is therefore more robust and easy to handle. At the same time, the closed-cell structure however also provides the possibility to cut the cushion from a material block or to process it. The danger for tools rotating at high rpm to risk an explosion of the grinding disc upon ingress of water and in particular in case of working under wet conditions can thus be eliminated. The limit values which are determined primarily by the centrifugal force for the working loads can be raised so that desirable and partially also prescribed safety margins can be observed or surpassed.

In this context, the limit loads in relation to the centrifugal force are no longer dependent on auxiliary structures for the strength as they are conventionally provided in the area of the working material face. The bottom side of the cushion can be provided with working materials, coupling agent structures or coupling agent layers without having to achieve therewith a safety contribution with respect to the centrifugal force strength.

In addition, with the reduced weight of the grinding disc, general advantages result for manufacture and storage, for the configuration of drive machines that must move less mass or enable smaller counterweights for compensation of mass vibrations and thereby also reduce the machine wear. However, the weight savings in the cushion, and thus on the tool, is in particular also beneficial for handling.

The special shape of an elastic plastic material foam, formed of closed-cell expanded and the thereby produced form of loose beads by heat and pressure to fused-together one-piece shaped bodies is in principle possible based on several thermoplastic elastomers that can be expanded to light particles. Particularly advantageous is the use of an elastomer on the basis of urethane (TPU) with which a thin-walled and thus lightweight, but still strong tenacious-elastic plastic material foam can be obtained. In addition, a correspondingly constructed plastic material foam on the basis of thermoplastic copolyamides (TPA), thermoplastic copolyester elastomers (TPC), thermoplastic copolyesters of hard and soft segments with chemical linking in the main chain by ether and/or ester groups, olefins, or styrene block copolymers are conceivable. Important in this context is a strong fusion of the particles of elastically adjusted material with each other which, in contrast to, for example, polystyrene hard foam materials for construction purposes with a rather brittle structure, provides a strong particle cohesion, wherein the particles themselves are elastically deformable as a result of their gas fill to be provided for expansion.

The particles that are gas-filled in the starting material are balloon-shaped, spherical or oval, but for fusing under pressure are however pressed against each other to such an extent that no or only very minimal intermediate spaces or interstices remain. Fusing under pressure is realized preferably by hot steam treatment in a pressing mold with which the particles are heated to the required glass transition range. The one-piece bodies which are generally obtained in closed molds can then subsequently be tempered by a subsequent temperature treatment in order to design them to be stress-free within and shape-stable.

With this shaping, cushions can be produced whose plastic material foam is homogenous and without a shell-type condensed outer molded skin up to the outer edges of the cushion. This uniformity in the structure of the plastic material foam avoids the outer molded skin which must be expediently provided in conventional open-pore integral foams and is provided as a protective envelope against moisture and dirt but is also susceptible in this configuration to becoming damaged. The elimination of a condensed outer molded skin is also beneficial to the properties of use of the tool because a predetermined elastic cushioning effect by the cushion up to the rim areas is provided and is not possibly impaired by the molded skin.

The working material face can be provided already during the molding process with a surface profiling for the connection of working material discs. This is a special feature of the thermoplastic elastomer material employed according to the invention as of closed-cell expanded and fused-together particles which makes it possible to produce particularly designed working material faces of the material itself upon pressure loading and fusing in a mold. In particular, in case of plastic material foams that are produced on the basis of urethane with expanded particles have been found to be suitable to create particular surface profilings.

In this respect, projections are to be produced in the working material face which are, for example, distributed across the surface area and which hook or engage a loop structure or textile structure on working material discs. This makes it obsolete to apply a separate layer with a coupling agent layer like a hook and loop surface with which thrust for surface finish machining along the working material face is to be transmitted.

Another advantage is a simple direct molding of working material discs or lamella elements as well as of hook and loop fastener layers or the like in the mold tool for molding with pressure and heat so that in the mold the particles not only with each other but also in the area of the working material face are connected with the other layer, without this requiring an additional working step.

The material is also suitable as a result of molding to integrally mold or embed further elements such as, for example, a fixed and stiff connecting part as it is conventional in particular for mechanically actuated tools with a coupling element for a machine drive, for example, with a central pin for clamping in a power drill. Such a connecting part is usually also further connected with a support member of metal or strong plastic material that covers the cushion at least partially across the surface in order to distribute the pressure to be transmitted to the cushion.

Alternatively, the tool can also be provided with a connecting part in the form of a grip element for manual actuation.

Embodiments of the invention are illustrated in the drawing and will be explained in the following in more detail. The figures show in:

FIG. 1 a cross-section of a tool according to the invention;

FIG. 2 view of the tool according to FIG. 1 at a slant from below;

FIG. 3 a detail cross section of the surface of the tool according to FIG. 2 in the direction of arrow III;

FIGS. 4, 5, and 6 further partial enlarged scale cross sections corresponding to FIG. 3 with other configurations of the surface;

FIG. 7 a cross-section of a further tool;

FIG. 8 view of the tool according to FIG. 7 at a slant from below.

The tool for surface finish machining illustrated in FIGS. 1 and 2 and identified as a whole by 1 represents a simple form of such a tool as a rotating grinding disc of rotation symmetry which (in case of surface finish machining from above) is provided at the bottom side with a working material face 2 and at the topside comprises a drive receptacle 3 which is to be clamped with a round pin 4 in a drill chuck of a power drill. The pin 4 of stronger material, preferably metal, passes into a support body 5 transmitting pressure and rotation forces of the drive and applied from above that supports a circular disk shaped elastic cushion 6 in flat connection on the bottom side. The cushion 6 itself forms with the bottom side the working material face 2. The cushion 6 projects radially past the plate-shaped support body 5 wherein a circumferential rim 7 is formed as a truncated cone between the circumference of the support body 5 and the working material face 2.

The tool 1 that in so far is described as conventional represents in its structure a particularly simple example. Other tools for surface finish machining can differ in regard to its construction, which, for example, can be provided with air channel guides and openings in the cushion, air channels in the area of the drive receptacle for suction removal of dust, which in the area of the drive receptacle is provided only with a knob or grip or several thereof for manual operation or which comprises, for the connection to machine drives, other couplings than a simple pin 4. It is also understood that not only rotating tools for surface machining are to be considered here, but also, as is conventional in practice, tools with oscillating movements along the surface to be machined or with wobble movements, as well as with random movements as they are naturally occurring in particular for manually operated tools for surface finish machining.

In these tools, a cushion such as the present cushion 6 has an important function for distribution of the pressure and for transferring movements between the working material face 2 and the drive receptacle 3, including its support body 5. In so far, the thickness of the cushion 6 is to be dimensioned in accordance with the intended deformations. In particular, the cushion 6 with regard to its stiffness or its yielding action is to be matched to the pressing forces. The energy uptake of the cushion during use may not lead to overheating or material destruction. The material of the cushion must be suitable to work under great loading with dust and dirt and also, in particular in case of wet grinding, under a great load of moisture. In addition, it is of interest when the cushion causes a minimal weight load for handling, in particular because it constitutes a significant volume proportion of the tool, wherein weight savings in principle are also advantageous in regard to the manufacture, shipment, and storage. In particular however, robustness and longevity are to be pursued for such a cushion, particularly because for tools of this kind the service life of the tool depends regularly on the cushion 6 when the working materials in the form of working material discs on the working material face 2 are provided to be exchangeable.

In practice, usually cushions of this kind are produced of a so-called “integral foam”, i.e., a polyurethane integral foam, that by mold-foaming in a mold, is provided with an open-cell core and a massive exterior skin toward the rim zones. This mold-foaming however provides no safety against ingress of moisture and dirt into the cushion, in particular also in case of damages of the exterior skin during use.

The cushion according to the invention employs in contrast thereto an elastic plastic material foam which is comprised of closed-cell expanded and fused-together particles of a thermoplastic elastomer (TPE). In the concrete example, the elastic plastic material foam is comprised of closed-cell expanded and fused-together particles of a thermoplastic polyurethane (E-TPU). This material that has been developed for different intended uses, i.e., for athletic shoe soles, has been found to be extremely advantageous as a cushion material. In contrast to the prior conventional integral foam, it has a uniform density up to the rim and can even be cut from greater material blocks. The elimination of condensed exterior skin areas provides already significant weight savings. In particular however, the thin-wall cell structure of the bead-like articles of which the plastic material foam is fused together, has a continuous lightweight as well as highly elastic structure of the material. The structure is closed-cell already based on the starting material and the closed-cell structure entails a reduced water absorption (and dirt absorption) so that even for working in wet conditions only 1 to 2% of volume are absorbed. The closed-cell structure of the elastic plastic material foam with gas volume enclosed therein by the expanding form material in the particles and thin cell walls provides a good elastic deformability which reduces the risk of material heating and material fatigue during use and also stands for a longevity of the cushion.

The working material face 2 can be provided in conventional way directly with a working material layer, for example, with grinding or polishing agents. In this context, the attachment of such working materials as well as the connection of the cushion 6 with the support body 5 can be realized in an advantageous manner already during molding of the cushion in a pressure mold so that an additional working step with fusing or gluing of flat layers to be joined is not needed. The adhesion of material integrally molded in the mold, inserted into a pressure mold that is then filled with the closed-cell expanded particles and then brought to fusing temperature with hot steam or another suitable medium, provides a complex tool configuration in a way that saves working steps.

Another advantageous property of the closed-cell cushion material of a thermoplastic elastomer resides the suitability for molding surface structures. In FIG. 2, on the working material face 2 a uniform structure with molded portions across the entire surface area is indicated, illustrated in FIG. 3 in an enlarged detail cross section in more detail. The working material face 2 is embodied with a pattern of uniformly distributed suction cups 8 which are directly molded in the material of the cushion 6. These suction cups 8 with downwardly open plate shape project from depressions 9 into which the suction cups 8 upon compression can be moved and which are framed by rim webs 10 which however end above the plane which is defined by the suction cups 8. The webs 10 delimit the movement of the suction cups in case of a pressure from the front when the suction cups, during working use, are pressure loaded after they had been placed onto a smooth back of a working material disc or another working material carrier. In so far, a coupling agent surface that can be directly formed from the cushion material is a cost-saving possibility for configuring the working material face. It is however understood that alternatively also a separate plate or disc with suction cups of the illustrated kind can be joined adhesively when molding the cushion 6 and can also be retrofitted by fusing or gluing.

FIG. 4 illustrates a configuration of the working material face with thorn-like projecting tips 11 as coupling agent layer that can engage, for example, a fabric or knitted fabric on the back of a working material disc and provides a loadable force connection between tool and working material for the rotating movement. The easily releasable coupling effect which is to be obtained thereby of a working material disc is sufficient for practical use with loadability in pressure and rotation direction.

FIGS. 5 and 6 show finely embodied configurations of a working material face in the meaning of a hook and loop fastener connection where knob-shaped projections 12 or 13 effect with mushroom-type, claw-shaped molded portions 14, 15 parallel to the working material face a barbed hook effect when the working material face molded in this way is engaging a corresponding open back structure of a working material disc or another working material carrier and thus produces a relatively strong yet still detachable connection between working material and tool.

The configurations of the working material face according to FIG. 4 to FIG. 6 can be obtained within a pressure mold which has a corresponding complementary configuration at the appropriate inner surfaces. Into this pressure mold, particles of a thermoplastic elastomer, for example, a thermoplastic polyurethane in before expanded form, are to be introduced as lose particles or beads, preferably in round or oval shape of a size of one or a few millimeters, and to be compressed with pressure from the loose bulk material to a compressed molded part that is strengthened by fusing by means of hot steam or another heating medium. After removal, this molded part can be tempered by a heat treatment in order to compensate internal stress and to stabilize the obtained shape.

A modified embodiment of the tool according to FIGS. 1 and 2 is illustrated in FIGS. 7 and 8 wherein the parts of the tool that are corresponding to each other are identified with the same reference numbers as before. In this further embodiment of the tool, the drive connector 3 is comprised of a central metal body 4 with topside inner thread in order to be screwed, for example, onto a drive spindle of a power drill. This metal body 4 is embedded into a support body 5 of solid plastic material which carries at the bottom side a cushion 6 of an elastic plastic material foam which is comprised of closed-cell expanded and fused-together particles of a thermoplastic elastomer (TPE). About a center axis 16, the cushion 6 is formed as a circular ring structure with a free inner recess into which partially a ring projection 17 of the support body 5 is projecting. In particular however, into the free inner chamber of the cushion 6 a central threaded projection 18 of the metal body 4 is projecting onto which from below a clamping nut 19 with externally cast-on plastic material clamping flange 20 can be screwed.

The clamping flange 20 can be screwed with the clamping nut 19 into the free inner space of the cushion 6 and countersunk in the recess. In this way, a working material disc can be secured in a simple way by clamping on the bottom working material face 2 of the cushion 6 which is provided in the area of the clamping flange 20 with a central hole and radial outwardly oriented slots in order to be able to deform the working material disc 21 for clamping with the clamping flange 20 and thus obtain a simple coupling connection with the cushion 6.

In comparison to the full-surface circular shape according to FIGS. 1 and 2, the inner recess of the cushion 6 has no significant effect on the operation of the tool 1 because the tools are used very often with rim-accentuated pressure application and because, in particular also for flat placement of the tool, the desired finish machining action primarily falls onto the radially farther outwardly positioned areas due to the outwardly higher rotational movements. 

What is claimed is: 1.-18. (canceled)
 19. A tool for surface finish machining, comprising: a cushion comprising a bottom side with a working material face provided with a working material or with a coupling agent configured to detachably connect a working material disc; a drive receptacle disposed at a top side of the cushion and configured to introduce working forces into the cushion; wherein the cushion is comprised of an elastic plastic material foam that is comprised of closed-cell expanded and fused-together particles of a thermoplastic elastomer.
 20. The tool according to claim 19, wherein the elastic plastic material foam is formed of a urethane-based elastomer.
 21. The tool according to claim 20, wherein the elastic plastic material foam is comprised of hard segments and soft segments, wherein the hard segments comprise urethane links and wherein the soft segments comprise links selected from the group consisting of ether links, ester links, and carbonate links.
 22. The tool according to claim 19, wherein the elastic plastic material foam is formed of thermoplastic polyamide elastomers.
 23. The tool according to claim 19, wherein the elastic plastic material foam is formed of thermoplastic copolyamides.
 24. The tool according to claim 19, wherein the elastic plastic material foam is formed of thermoplastic copolyesters.
 25. The tool according to claim 19, wherein the elastic plastic material foam is formed of thermoplastic olefin elastomer.
 26. The tool according to claim 19, wherein the elastic plastic material foam is formed of thermoplastic styrene block copolymers with a diene.
 27. The tool according to claim 19, wherein the elastic plastic material foam is formed of gas-filled, balloon-shaped, approximately spherical to oval particles joined under pressure and fused with each other at their surfaces under heat.
 28. The tool according to claim 19, wherein the elastic plastic material foam is homogenous and embodied without a condensed outer molded skin up to outer rims of the cushion.
 29. The tool according to claims 19, wherein the working material face is provided with a surface profiling configured to attach a working material disc thereto.
 30. The tool according to claim 29, wherein the surface profiling comprises projections that are distributed across a surface of the working material face and configured to hook or engage a loop texture or fabric texture of a working material disc.
 31. The tool according to claim 29, wherein the surface profiling is comprised of suction cups distributed across a surface of the working material face.
 32. The tool according to claim 19, wherein the drive receptacle comprises at least one fixed and stiff connecting part that is integrally formed on the cushion during molding of the cushion.
 33. The tool according to claim 32, wherein the connecting part comprises a coupling element for a machine drive and a support body that at least partially covers the cushion.
 34. The tool according to claim 32, wherein the connecting part comprises at least one grip element configured to manually actuate the tool.
 35. The tool according to claim 19, wherein the coupling agent is integrally formed on the working material face during molding of the cushion.
 36. The tool according to claim 19, wherein the working material is integrally formed during molding of the cushion on the working material face. 